1. Technical Field of the Invention
The present invention relates to the treatment of edible crops and, in particular, to pre-harvest treatment of such crops.
2. Description of the Prior Art
A very large proportion of edible crops are irrigated by overhead sprays. Crops grown in proximity of urban areas may utilize potable mains water for this use. However, due to the expansion of urban population traditional vegetable growing areas are being displaced to areas where irrigation supplies are dependant on dams or rivers. Surface water as above is contaminated by livestock, poultry and misdirected sewage effluent. This contamination results in a growth of undesirable human pathogens in the water supply. The trend to recycle drainage water and run off from the growing area to conserve water, results in increasing the level of plant pathogens in the irrigation supply. Total Plate Count (TPC) of this water will give a typical figure of 106 of Colony Forming Units CFU/ml indicating a high level of contamination. In addition, faecal contamination will show coliform counts of 101-103 ml.
In developed countries, the general requirements for ready-to-eat foods is for a TPC of 103/gm or less and nil coliforms. Quite obviously, the contaminated irrigation water is not helping achieve the food safety requirement.
A further issue in terms of food safety is pesticide residues. As most vegetable crops require generous watering this increases the humidity adjacent the crop and, in turn, results in prime conditions for fungal diseases.
Many of these diseases develop very rapidly and a whole crop can be wiped out in a few days.
While a pesticide spray would control the fungal problem it may leave a residue on the crop at harvest.
The residue, at the time of harvest, cannot exceed the Maximum Residue Level (MRL). To avoid exceeding the MRL a time interval is determined between spraying the pesticide and harvest. This time is called the Withholding Period.
Consequently, if a fungal problem occurs close to harvest it may not be possible to use any pesticide on the crop because of the withholding period.